I have two double rifles in the above calibers. I am going to use 10.3x60R in the 400 and have Bertram brass for the 500/450 magnum. The new cases fit fine in the double rifles. I don't want to wait 6 months and pay hundreds of dollars for dies. Are there any easily available dies that I can use to neck size and seat the bullets? An example would be using .458 Winchester dies to load .450 3 1/4 straight, as long as full length resizing isn't needed. Obviously need the correct size for the bullet diameter. Am I barking up the wrong tree?

Because cases tend to stretch in a double, neck sizing may only work with new brass. Also because there may be slight differences in each chamber by only neck sizing after firing the rounds may not chamber properly.

Thanks srose, I thought of that also. I am not a hunter and only want to work up a few loads. I can get by with using seperate cases for each chamber and I can trim them, Again thanks for your post.